Flat panel display devices have replaced cathode ray tube (CRT) display devices as the mainstream display device in the display marketplace. One type of flat panel display device is the liquid crystal (LCD) device. FIG. 1 shows a cross-sectional view of a conventional LCD panel 100, which includes a substrate 120, an opposite substrate 110, an alignment layer 130, an alignment layer 140 and a liquid crystal layer 150. The alignment layer 130 is disposed on the opposite substrate 110, while the alignment layer 140 is disposed on the substrate 120. The material of the alignment layers 130 and 140 includes polyimide. The liquid crystal layer 150 is sealed between the opposite substrate 110 and the substrate 120.
When an electrical potential is applied between the opposite substrate 110 and the substrate 120, the liquid crystal molecules of the liquid crystal layer 150 are rotated by the strength of the applied potential for enabling the LCD panel 100 to have light transmittance according to the voltage. As a result, the LCD panel 100 is able to display frames with various gray values according to the potential applied between the opposite substrate 110 and the substrate 120.
The main function of the alignment layers 130 and 140 is to provide the boundary conditions required for stabilizing the liquid crystal molecules of the liquid crystal layer 150, so that the liquid crystal molecules of the liquid crystal layer 150 are arranged along a particular direction and order. Conventional alignment layers, however, are unable to effectively stabilize the liquid crystal molecules positioned at the boundary of the liquid crystal layer 150 due to the restriction in both the structure and the material of the alignment layers 130 and 140.
When an electrical potential is applied between the substrate 120 and the opposite substrate 110, the response rate of the liquid crystal molecules of the liquid crystal layer 150 is slowed down. When the liquid crystal display panel 100 attempts to display continuous frames, a noticeable discontinuous frame effect can easily occur, which can result in user dissatisfaction. Apart from the problem of slow response rate, the liquid crystal molecules of the liquid crystal layer 150 may even be rotated erroneously when the boundary conditions are unstable, causing deterioration of the display quality of the LCD panel 100. To resolve the above-identified problems, a method for reducing the stabilization time for liquid crystal molecules is provided in the U.S. Pat. No. 6,043,860. The method stabilizes the liquid crystal molecule positioned at the boundary of the liquid crystal layer 150 and increases the response rate of the liquid crystal molecules by adding monomers into the liquid crystal layer 150.
In addition to slow response rates of liquid crystal molecules, LCD devices also face the hurdle of achieving wider viewing angles. For example, the alignment layers 130 and 140 normally have to go through several rubbing treatments before liquid crystal molecules of the liquid crystal layer 150 are able to provide multi-directional alignment effect. However, this practice, which usually produces limited multi-directional alignment effect, makes the manufacturing process more complicated, which can result in a low yield rate.
Another approach for achieving the multi-directional alignment effect for liquid crystal molecules of the LCD panel 100 is to incorporate photo-alignment material into the alignment layers 130 and 140. However, the photo-alignment material may not be stable, and exposure equipment required to provide the photo-alignment material in the manufacturing process is expensive and complicated.
Another conventional approach of providing the multi-directional alignment effect is by forming protrusions on the alignment layers 130 and 140, forming a patterned slit on the pixel electrode of the substrate 120, or forming both the protrusions and the slit. However, this practice requires an extra mask step in the manufacturing process, which leads to increased manufacturing cost and reduced yield rate.